All over the city, innocent people are being mysteriously abducted, never to be seen again. During his investigations of these incidents, Shinji Kido – an intern at the online news service ORE Journal – discovers one of the Advent Card decks at an apartment where every reflective surface has been covered by newspaper. He is soon sucked into the Mirror World, discovering the terrifying truth behind the disappearances: people are literally being pulled through mirrors by the monsters of the Mirror World so that they may feed. He is about to be killed by a powerful dragon named Dragredder when he is saved by Kamen Rider Knight: Ren Akiyama. Ren seeks to win the Rider War at all costs. He works with a young woman named Yui Kanzaki, who seeks her missing brother: the master of the Rider War, Shiro Kanzaki. Seeing Ren's strength, Shinji enters the Rider War not for the prize, but so that he may protect innocent people from the threat of the Mirror World, and stop the senseless fighting between the Kamen Riders. With Dragredder as his Contract Monster, he becomes Kamen Rider Ryuki.

The Mirror Monsters (ミラーモンスター,Mirā Monsutā) are entities created by Yui as drawings made by her and her brother when they were young and given life by Yui's mirror-self. As these creatures have no true life of their own, they prey on humans to survive on their lifeforce. The only human they cannot attack is Yui herself, whom they obey absolutely like Kanzaki. However, rogue Mirror Monsters who attack Yui are countered by Kamen Rider Odin or a loyal Mirror Monster who serves Kanzaki. However, the majority of the monsters are contracted allies and the power source for most of the thirteen Kamen Riders, building their power by absorbing the energy of other defeated Mirror Monsters, but if the energy is not absorbed, it reforms into a new Mirror Monster. But once their master is killed, they simply go after the one who killed them.

Kamen Rider Ryuki Special: 13 Riders(仮面ライダー龍騎スペシャル 13RIDERS,Kamen Raidā Ryūki Supesharu Sātīn Raidāzu) was written by Toshiki Inoue and directed by Ryuta Tasaki. It features the debut of the thirteenth Kamen Rider in the continuity of Ryuki: Verde. This special was first broadcast on TV Asahi on September 19, 2002.[1][2] It was later released on DVD on July 21, 2003.[3] The DVD also featured information on the characters, an interview with actor Arthur Kuroda, and an "interview" with some of the characters.

This television special is an alternate telling of the Kamen Rider Ryuki story. Shinji Kido's life, working as an employee at ORE Journal, takes a sharp turn after being pulled into the Mirror World by a Mispider. Luckily, he was saved by a Kamen Rider, Ryuki (Koichi Sakakibara, portrayed by Keiichi Wada). However, Sakakibara could no longer go on due to the severity of his injuries and passed his Card Deck to Shinji, allowing him to become the next Ryuki and defeat the monster. After meeting with Yui Kanzaki and Ren Akiyama (Kamen Rider Knight), Shinji learns about the conditions of the Rider War, as well as of the other Riders participating. Unable to allow such a game of death to exist like his Rider predecessor, Shinji sets out to convince all the Riders to end the senseless fighting and put an end to the War. His pleas fall upon deaf ears as just about every other Rider (except for the already-defeated Riders Raia and Scissors) sets out to hunt down Shinji and his eventual reluctant ally, Ren. Eventually, Shinji's deck is destroyed and Ren dies, after passing on the deck for Kamen Rider Knight to Shinji. The special has two different endings which were voted on by the viewers via phone at the time of the initial airing: the voted-for-air ending (in which Shinji faces the surviving Riders on his own) and the alternate ending (a resetting of the Rider War).

Kamen Rider Ryuki the Movie: Episode Final(劇場版 仮面ライダー龍騎 EPISODE FINAL,Gekijōban Kamen Raidā Ryūki Episōdo Fainaru) is an alternate ending to the series, taking place after the events of episode 46. With only six Riders remaining in the Rider War; Ryuki (Shinji Kido), Knight (Ren Akiyama), Zolda (Shuichi Kitaoka), Ouja (Takeshi Asakura), and Femme (Miho Kirishima); Shiro Kanzaki alerts them to quickly settle the Rider War within three days. One of them must win and become the last survivor before the sixth surviving Rider reveals himself. Amidst the impending chaos of the fight between the Riders, Shinji discovers an unbelievable truth about the relationship between Yui Kanzaki and the Mirror World, as well as discovering the existence of his Mirror World doppelganger, Kamen Rider Ryuga.

Kamen Rider Ryuki: Ryuki vs. Kamen Rider Agito(仮面ライダー龍騎 龍騎vs仮面ライダーアギト,Kamen Raidā Ryūki Ryūki Bui Esu Kamen Raidā Agito) is the Ryuki Hyper Battle Video. It features Shinji Kido having a dream where he joins up with Kamen Riders Knight, Zolda, and Ouja, all of whom who are acting out of character, to fight an evil Kamen Rider Agito in the Mirror World. They are soon joined by the real Kamen Rider Agito who helps defeat his evil doppelganger.

Ryuki had two separate S.I.C. Hero Saga side stories published in Monthly Hobby Japan magazine. The first was titled Masked Rider Ryuki: Advent Calendar(MASKED RIDER RYUKI -アドベントカレンダー-,Kamen Raidā Ryūki -Adobento Karendā-) and featured original characters Kamen Rider Ouja Survive (仮面ライダー王蛇サバイブ,Kamen Raidā Ōja Sabaibu) and his Mirror Monster the Genosurviver (ジェノサバイバー,Jenosabaibā). The second S.I.C. Hero Saga story Masked Rider Ryuki: World of If(MASKED RIDER RYUKI -IFの世界-,Kamen Raidā Ryūki -Ifu no Sekai-) is an alternate telling that features Ouja Survive from Advent Calendar and also introduces Kamen Rider Ryuga Survive (仮面ライダーリュウガサバイブ,Kamen Raidā Ryūga Sabaibu). Advent Calendar ran from August to December 2004 and World of If ran from June to August 2005.

A video game based on the series, developed by Digifloyd and published by Bandai, was released in Japan during 2002 for the PlayStation. It is a basic fighting game where all thirteen Riders are playable with all the forms seen in the show, movie and specials (with the exception of the Alternatives and Ouja's Blank Form, seen in EPISODE FINAL). Four of the Contract Monsters (Volcancer, Metalgelas, Destwilder and Gigazelle), the two Zebraskulls (Iron and Bronze) and Megazelle are also playable.

In addition to the Kamen Rider: Dragon Knight adaptation, Ryuki has been broadcast in its original form in many languages and nations. It was dubbed into Korean as Masked Rider Dragon (가면라이더 드래건Gamyeon Raideo Deuraegeon) in South Korea on January 14, 2005,[5]Filipino in the Philippines as Masked Rider Ryuki on ABS-CBN 2, Malay on NTV7, and in Indonesian on RCTI and Indosiar. It is also the first ever Kamen Rider Series to be dubbed in Arabic after its run on Space Toon.